Spell Flux is exceptionally powerful against opponents standing in the middle of their minion waves.
Using Ryze's ultimate to farm creeps can lead to a large gold advantage.
Use Rune Prison to guarantee a hit with Overload.
Weaving Overload between other spellcasts while supercharged by Arcane Mastery allows Ryze to deal maximum damage during this period.
Be cautious about engaging Ryze alone with less than full Health.
Cleanse and Banshee's Veil are especially effective defenses against Ryze.
Ryze can only lock down one player with Rune Prison. Attacking with friends is the most effective approach, but remember to avoid Spell Flux bouncing between you and your allies.